17,630 research outputs found
Singular Fermi Surfaces I. General Power Counting and Higher Dimensional Cases
We prove regularity properties of the self-energy, to all orders in
perturbation theory, for systems with singular Fermi surfaces which contain Van
Hove points where the gradient of the dispersion relation vanishes. In this
paper, we show for spatial dimensions that despite the Van Hove
singularity, the overlapping loop bounds we proved together with E. Trubowitz
for regular non--nested Fermi surfaces [J. Stat. Phys. 84 (1996) 1209] still
hold, provided that the Fermi surface satisfies a no-nesting condition. This
implies that for a fixed interacting Fermi surface, the self-energy is a
continuously differentiable function of frequency and momentum, so that the
quasiparticle weight and the Fermi velocity remain close to their values in the
noninteracting system to all orders in perturbation theory. In a companion
paper, we treat the more singular two-dimensional case.Comment: 48 pages LaTeX with figure
Quantized Non-Abelian Monopoles on S^3
A possible electric-magnetic duality suggests that the confinement of
non-Abelian electric charges manifests itself as a perturbative quantum effect
for the dual magnetic charges. Motivated by this possibility, we study vacuum
fluctuations around a non-Abelian monopole-antimonopole pair treated as point
objects with charges g=\pm n/2 (n=1,2,...), and placed on the antipodes of a
three sphere of radius R. We explicitly find all the fluctuation modes by
linearizing and solving the Yang-Mills equations about this background field on
a three sphere. We recover, generalize and extend earlier results, including
those on the stability analysis of non-Abelian magnetic monopoles. We find that
for g \ge 1 monopoles there is an unstable mode that tends to squeeze magnetic
flux in the angular directions. We sum the vacuum energy contributions of the
fluctuation modes for the g=1/2 case and find oscillatory dependence on the
cutoff scale. Subject to certain assumptions, we find that the contribution of
the fluctuation modes to the quantum zero point energy behaves as -R^{-2/3} and
hence decays more slowly than the classical -R^{-1} Coulomb potential for large
R. However, this correction to the zero point energy does not agree with the
linear growth expected if the monopoles are confined.Comment: 18 pages, 5 figures. Minor changes, reference list update
Resonance modes in a 1D medium with two purely resistive boundaries: calculation methods, orthogonality and completeness
Studying the problem of wave propagation in media with resistive boundaries
can be made by searching for "resonance modes" or free oscillations regimes. In
the present article, a simple case is investigated, which allows one to
enlighten the respective interest of different, classical methods, some of them
being rather delicate. This case is the 1D propagation in a homogeneous medium
having two purely resistive terminations, the calculation of the Green function
being done without any approximation using three methods. The first one is the
straightforward use of the closed-form solution in the frequency domain and the
residue calculus. Then the method of separation of variables (space and time)
leads to a solution depending on the initial conditions. The question of the
orthogonality and completeness of the complex-valued resonance modes is
investigated, leading to the expression of a particular scalar product. The
last method is the expansion in biorthogonal modes in the frequency domain, the
modes having eigenfrequencies depending on the frequency. Results of the three
methods generalize or/and correct some results already existing in the
literature, and exhibit the particular difficulty of the treatment of the
constant mode
Seasonal reproduction in a fluctuating energy environment: Insolation-driven synchronized broadcast spawning in corals
*Background/Question/Methods:* Colonies of spawning corals reproduce in mass-spawning events, in which polyps within each colony release sperm and eggs for fertilization in the water column, with fertilization occurring only between gametes from different colonies. Participating colonies synchronize their gamete release to a window of a few hours once a year (for the species Acropora digitifera we study experimentally). This remarkable synchrony is essential for successful coral reproduction and thus, maintenance of the coral reef ecosystem that is currently under threat from local and global environmental effects such as pollution, global warming and ocean acidification. The mechanisms determining this tight synchrony in reproduction are not well understood, although several influences have been hypothesized and studied including lunar phase, solar insolation, and influences of temperature and tides. Moreover, most corals are in a symbiotic relationship with photosynthetic algae (Symbiodinium spp.) that live within the host tissue. Experiments supported by detailed bioenergetic modeling of the coral-algae symbiosis have shown that corals receive >90% of their energy needs from these symbionts. We develop a bioenergetic integrate-and-fire model in order to investigate whether annual insolation rhythms can entrain the gametogenetic cycles that produce mature gametes to the appropriate spawning season, since photosynthate is their primary source of energy. We solve the integrate-and-fire bioenergetic model numerically using the Fokker-Planck equation and use analytical tools such as rotation number to study entrainment.

*Results/Conclusions:* In the presence of short-term fluctuations in the energy input, our model shows that a feedback regulatory mechanism is required to achieve coherence of spawning times to within one lunar cycle, in order for subsequent cues such as lunar and diurnal light cycles to unambiguously determine the “correct” night of spawning. Entrainment to the annual insolation cycle is by itself not sufficient to produce the observed coherence in spawning. The feedback mechanism can also provide robustness against population heterogeneity due to genetic and environmental effects. We also discuss how such bioenergetic, stochastic, integrate-and-fire models are also more generally applicable: for example to aquatic insect emergence, synchrony in cell division and masting in trees
Preliminary design study of nuclear Brayton cycle/Heat Exchanger and Duct Assembly /HXDA/, phase 3 Topical report
Nuclear Brayton cycle heat exchanger and duct assembl
Nonpayment of Production Royalties under a Producers 88 Lease: A Legislative Prescription to Cure a New Disease
Finite Temperature Spectral Densities of Momentum and R-Charge Correlators in Yang Mills Theory
We compute spectral densities of momentum and R-charge correlators in thermal
Yang Mills at strong coupling using the AdS/CFT correspondence. For
and smaller, the spectral density differs markedly from
perturbation theory; there is no kinetic theory peak. For large , the
spectral density oscillates around the zero-temperature result with an
exponentially decreasing amplitude. Contrast this with QCD where the spectral
density of the current-current correlator approaches the zero temperature
result like . Despite these marked differences with perturbation
theory, in Euclidean space-time the correlators differ by only from
the free result. The implications for Lattice QCD measurements of transport are
discussed.Comment: 18 pages, 3 figure
Investigations on T violation and CPT symmetry in the neutral kaon system -- a pedagogical approach --
During the recent years experiments with neutral kaons have yielded
remarkably sensitive results which are pertinent to such fundamental phenomena
as CPT invariance (protecting causality), time-reversal invariance violation,
coherence of wave functions, and entanglement of kaons in pair states. We
describe the phenomenological developments and the theoretical conclusions
drawn from the experimental material. An outlook to future experimentation is
indicated.Comment: 41 pages, 9 figures. See arXiv:hep-ph/0603075 for an enlarged versio
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Numerical modelling of microwave sintering of lunar simulants under near lunar atmospheric condition
An interacting quark-diquark model of baryons
A simple quark-diquark model of baryons with direct and exchange interactions
is constructed. Spectrum and form factors are calculated and compared with
experimental data. Advantages and disadvantages of the model are discussed.Comment: 13 pages, 3 eps-figures, accepted by Phys.Rev. C Rapid Communication
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